1. Field of the Invention
The present invention relates to a manufacturing method for a magnetic head including a main pole and a write shield.
2. Description of Related Art
The recording systems of magnetic recording devices such as magnetic disk drives include a longitudinal magnetic recording system in which the magnetization of signals is directed along the plane of a recording medium (the longitudinal direction), and a perpendicular magnetic recording system in which the magnetization of signals is directed perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistance element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on the top surface of a substrate.
A magnetic head for use in a magnetic disk drive is typically incorporated in a slider. The slider has a medium facing surface configured to face a recording medium. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is configured to slightly fly over the surface of the recording medium by means of an airflow that comes from the leading end into the space between the medium facing surface and the recording medium. The recording medium includes a magnetic recording layer. Tracks are concentrically formed in the magnetic recording layer. The tracks are the area of the magnetic recording layer on which data is to be written.
The write head unit includes a main pole. The main pole has an end face located in the medium facing surface, and produces, from the end face, a write magnetic field in a direction perpendicular to the plane of the recording medium.
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs depending on the position of the magnetic head across the tracks.
Particularly, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, there may occur the phenomenon that signals already written on one or more tracks in the neighborhood of a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. Unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). Unwanted erasure is noticeably encountered upon occurrence of a skew. For enhancement of recording density, it is necessary to prevent unwanted erasure.
A known technique for preventing unwanted erasure and enhancing the recording density is to provide a wrap-around shield and a gap section, the wrap-around shield being a write shield having an end face that is located in the medium facing surface and surrounds the end face of the main pole, the gap section separating the wrap-around shield from the main pole. This technique is disclosed in, for example, U.S. Pat. Nos. 8,472,137 B2, 8,427,781 B1 and 8,289,649 B2.
The wrap-around shield includes a leading shield, first and second side shields, and a trailing shield. The leading shield has an end face located in the medium facing surface at a position on the leading side of the end face of the main pole. The first and second side shields have two end faces located in the medium facing surface at positions on opposite sides of the end face of the main pole in the track width direction. The trailing shield has an end face located in the medium facing surface at a position on the trailing side of the end face of the main pole.
The gap section includes a leading gap section for separating the leading shield from the main pole, first and second side gap sections for separating the first and second side shields from the main pole, and a trailing gap section for separating the trailing shield from the main pole.
The wrap-around shield has the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, and thereby preventing the magnetic flux from reaching the recording medium. A magnetic head provided with the wrap-around shield is able to prevent unwanted erasure and provide further enhanced recording density.
The position of an end of a record bit to be recorded on the recording medium is determined by the position of the trailing-side edge (hereinafter referred to as the top edge) of the end face of the main pole in the medium facing surface. Accordingly, what are important for enhancing the write characteristics of the write head unit include: high write magnetic field strength at the top edge or in the vicinity thereof; and a large gradient of change in the write magnetic field strength at the top edge or in the vicinity thereof in the distribution of the write magnetic field strength in the direction in which the tracks extend. High write magnetic field strength at the top edge or in the vicinity thereof contributes to the enhancement of overwrite property. A large gradient of change in the write magnetic field strength at the top edge or in the vicinity thereof contributes to the reduction of bit error rate.
A magnetic head provided with the wrap-around shield suffers from the problem that when a large amount of magnetic flux leaks from the main pole to the wrap-around shield, particularly to the leading shield and the first and second side shields, there occurs reductions in the write magnetic field strength and the aforementioned gradient of change at the top edge of the end face of the main pole or in the vicinity of the top edge, and the write characteristics are thereby degraded.
Now, we will discuss a configuration in which the thickness of the leading gap section is constant regardless of distance from the medium facing surface. First, assume that the thickness of the leading gap section is small. In this case, the end face of the main pole and the end face of the leading shield are at a small distance from each other in the medium facing surface. Thus, the write shield can fully perform the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium. However, because of the small distance between the main pole and the leading shield, flux leakage from the main pole to the leading shield increases to degrade the write characteristics.
Next, assume that the thickness of the leading gap section is large. In this case, it is possible to reduce flux leakage from the main pole to the leading shield. However, because of a large distance between the end face of the main pole and the end face of the leading shield in the medium facing surface, the write shield cannot perform its function satisfactorily.
In the magnetic head disclosed in U.S. Pat. No. 8,427,781 B1, the main pole has a bottom end located at the leading-side edge. The bottom end includes a first inclined portion, a first flat portion, a second inclined portion, and a second flat portion arranged in this order, the first inclined portion being closest to the medium facing surface. In this magnetic head, the leading shield has a first inclined surface opposed to the first inclined portion, and a second inclined surface located farther from the medium facing surface than the first inclined surface. The distance between the second inclined surface and the second inclined portion is greater than the distance between the first inclined surface and the first inclined portion.
In the magnetic head disclosed in U.S. Pat. No. 8,427,781 B1, a step exists between the first inclined portion and the second inclined portion at the bottom end of the main pole. In this magnetic head, due to the existence of the step, the main pole is small in volume and magnetic flux is likely to leak out of the main pole. These factors result in degradation of the write characteristics of the magnetic head.
U.S. Pat. No. 8,289,649 B2 discloses a manufacturing method for a magnetic head as follows. According to the manufacturing method, a mold is formed on the top surface of the leading shield by photolithography. The mold includes first and second receiving sections for receiving the first and second side shields, and a midsection located between the first receiving section and the second receiving section. Then, the first and second side shields are formed by plating so as to be received in the first and second receiving sections. The mold is then removed. Then, a gap layer is formed. The gap layer includes a leading gap section and first and second side gap sections. Then, the main pole is formed.
This manufacturing method is likely to generate a gap between the midsection of the mold and the top surface of the leading shield. If the gap is generated, a magnetic material used for forming the first and second side shields gets into the gap in the process of forming the first and second side shields. This results in the formation of unwanted coupling section coupling the first and second side shields to each other. In such a case, disadvantageously, the main pole becomes smaller in volume and the write characteristics of the magnetic head are thus degraded.